Alright. It is true, that messages engraved in stones has survived for thousands of ears. It is the only proven method for sending information in the very far future. I may engrave messages on some stones in my spare time. It is easy and cheap. Stones on the ground are for free. Some people are even paying for stones to be removed from their gardens. Now it only remains the problem how to write so much information - the times, dates and places for the time travelers to come.